Magnetic storage media with Ag, Au-containing magnetic layers

ABSTRACT

A magnetic recording medium having a Au, Ag-containing magnetic layer having Co, Cr, Ag and Au; the magnetic recording layer having Co-containing magnetic grains surrounded by substantially nonmagnetic Cr-containing grain boundaries; wherein said Ag and said Au are substantially immiscible in the Co-containing magnetic grains is disclosed.

RELATED APPLICATIONS

This application is related to application Ser. No. 10/827,421, filedApr. 20, 2004, entitled “Magnetic Recording Media with Cu-ContainingMagnetic Layers,” which is incorporated herein by reference.

FIELD OF INVENTION

The present invention relates to improved, high recording performancemagnetic recording media comprising at least one Ag or Au-containingmagnetic recording layer for improved segregation for obtaining sharpertransitions between the magnetic grains and non-magnetic Cr-rich grainboundaries. More particularly, the invention relates to hard diskrecording media with increased saturation magnetization (Ms) andmagnetocrystalline anisotropy and narrower intrinsic switching fielddistribution.

BACKGROUND

Thin film magnetic recording media, wherein a fine-grainedpolycrystalline magnetic alloy layer serves as the magnetic recordinglayer, are generally classified as “longitudinal” or “perpendicular,”depending on the orientation of the magnetic domains (bits) of thegrains in the magnetic recording layer. FIG. 1, obtained from MagneticDisk Drive Technology by Kanu G. Ashar, 322 (1997), shows magnetic bitsand transitions in longitudinal and perpendicular recording.

The increasing demands for higher a real recording density imposeincreasingly greater demands on thin film magnetic recording media interms of coercivity (Hc), remanent coercivity (Hcr), magnetic remanance(Mr), which is the magnetic moment per unit volume of ferromagneticmaterial, coercivity squareness (S*), signal-to-medium noise ratio(SMNR), and thermal stability of the media. These parameters areimportant to the recording performance and depend primarily on themicrostructure of the materials of the media. For example, as the SMNRis reduced by decreasing the grain size or reducing exchange couplingbetween grains, it has been observed that the thermal stability of themedia decreases.

Conventionally used storage media contain a magnetic recording layerhaving Co—Cr—Pt—B and Co—Cr—Ta alloys where B and Ta are mainly used toimprove the segregation of Cr in the magnetic layer. A bettersegregation profile of Cr leads to a sharper transition between themagnetic grains and the non-magnetic Cr-rich grain boundaries, and thus,the recording media is expected to have higher saturation magnetization,Ms and magnetocrystalline anisotropy and narrower intrinsic switchingfield distribution.

As the storage density of magnetic recording disks has increased, theproduct of Mr and the magnetic layer thickness t has decreased and Hcrof the magnetic layer has increased. This has led to a decrease in theratio Mrt/Hcr. To achieve a reduction in Mrt, the thickness t of themagnetic layer has been reduced, but only to a limit because themagnetization in the layer becomes susceptible to thermal instability.This instability has been attributed to thermal activation of smallmagnetic grains (the super-paramagnetic effect). Such thermalinstability can cause undesirable decay of the output signal of themagnetic recording medium and data loss.

The thermal stability of a magnetic grain is to a large extentdetermined by K_(u)V, where K_(u) is the magnetic anisotropy constant ofthe magnetic layer and V is the volume of the magnetic grain. As themagnetic layer thickness is decreased, V decreases. Thus, if themagnetic layer thickness is too thin, the stored magnetic informationmight no longer be stable at normal disk drive operating conditions.

One proposed solution to the problem of thermal instability is toincrease K_(u). However, the increase in K_(u) is limited to the pointwhere the coercivity H_(c), which is approximately equal to K_(u)/Mr,becomes too large to be written by a conventional recording head. On theother hand, a reduction in Mr of the magnetic layer for a fixed layerthickness is limited by the coercivity that can be written. Increasing Vby increasing inter-granular exchange can also increase thermalstability. However, this approach could result in a reduction in theSMNR of the magnetic layer.

Thus, there is a need for new materials for the magnetic recording layerthat provide increased grain segregation in the magnetic layer, leadingto higher Ms and improved recording performance.

SUMMARY OF THE INVENTION

The embodiments of the invention are directed to a longitudinal orperpendicular recording medium having an improved segregation within themagnetic layers having Ag, Au-containing layers. Ag and Au has lowmiscibility with Co at temperatures below 573 K. Results show that mediawith Au, Ag-containing magnetic layers have higher Ms and improvedrecording performance.

As will be realized, this invention is capable of other and differentembodiments, and its details are capable of modifications in variousobvious respects, all without departing from this invention.Accordingly, the drawings and description are to be regarded asillustrative in nature and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows (a) longitudinal and (b) perpendicular recording bits.

FIG. 2 shows enthalpies of solution of solid X═Cu, Ag, Au in Y═Co, Pt,Cr and B.

DETAILED DESCRIPTION

Magnetic layer without Au and Ag will be called “non Au or Ag-containingmagnetic layer,” ML, and magnetic layers with Au and Ag will be called“Au, Ag-containing magnetic layer,” AuAgML.

Magnetic recording media having Co—Cr—Pt—B and Co—Cr—Ta alloys contain Band Ta to improve the segregation of Cr in the magnetic layer. A bettersegregation profile of Cr leads to a sharper transition between themagnetic grains and the non-magnetic Cr-rich grain boundaries, and thus,the recording media is expected to have higher saturation magnetization(Ms) and magnetocrystalline anisotropy (K_(u)) and narrower intrinsicswitching field distribution.

The embodiments of the present invention are based upon recognition thatthe improvement in segregation profile of Cr atoms in CoCr-based alloymagnetic layers upon addition Ta and/or B thereto is not necessarilysufficient to provide media required able to satisfy the ever-increasingperformance criteria and parameters required of high-performancemagnetic disk recording media utilized in computer-related applications.

In pursuit of improved segregation within the magnetic layers Au,Ag-containing layers were investigated. Au and Ag were selected becauseof their low miscibility with Co at temperatures below 573 K. Theembodiments of present invention are based upon the unexpected resultsof this invention that the addition of Au and Ag in the magnetic alloyof the magnetic recording medium further improves the segregationbehavior and provides magnetic recording media with even sharpertransitions (i.e., segregation profiles) between Co-containing magneticgrains and Cr-rich, non-magnetic grain boundaries than attainable by Taand/or B additions to CoCr. Such embodiments of this invention resultedin improved media exhibiting increased M_(s) and magnetocrystallineanisotropy and narrower intrinsic switching field distribution.

As a preliminary aspect of the investigation resulting in the presentinvention, the enthalpies of solution of solid X═Cu, Ag, Au in Y═Co, Pt,Cr and B (amount of X atoms is assumed to be so small so that all Xatoms are surrounded only by Y atoms in the solution) was calculatedfollowing the procedure of A. R. Miedema, Physica B 182, 1 (1992). Theresults of the calculation are shown in FIG. 2.

In FIG. 2, please note that if H_(sol) of X in Y is positive X does notlike to mix with Y and if H_(sol) is negative X likes to mix with Y. Theresults shown graphically in FIG. 2 demonstrate the following:

-   (1) Cu does not like to mix with Co and Cr and like to mix with Pt    and B;-   (2) Ag does not like to mix with Co, Cr and B and like to mix with    Pt; and-   (3) Au does not like to mix with Co and Pt and like to mix with Cr    and B.

CoCrPtB recording media contains CoPt-rich magnetic grains surrounded bynonmagnetic (or weakly magnetic) Cr rich grain boundaries as has beenexplained in Werner Grogger, Kannan M. Krishnan, Roger A. Ristau, ThomasThomson, Samuel D. Harkness, Rajiv Ranjan, Appl. Phys. Lett. 80, 1165(2002). If CoCrPtB recording media has large concentration of B,preferential segregation of B in grain boundaries has been observed.From FIG. 2, it would be expected that Ag and Au will avoid CoPt richregions (magnetic grains). Moreover, from FIG. 2 it would appear that Agwould also avoid Cr(B) rich regions as well while Au will prefer Cr(B)regions (grain boundaries). The applicants thus concluded that both Agand Au may be used to improve segregation in CoCrPtB recording media.However, since Au likes to mix with Cr(B) it would be expected that Auwould be more uniformly distributed in the grain boundary regions andtherefore it would be expected that Au would provide better magneticgrain isolation than Ag. From FIG. 2, one cannot predict position of Cuin CoCrPtB recording media.

Based on the above understanding of the miscibility of Au and Ag inCoCrPtB-containing magnetic recording layer, the embodiments of thisinvention for longitudinal and perpendicular media could be thefollowing.

Longitudinal recording media:

-   1. Substrate-   2. Non-magnetic seed and under layers, UL, capable of controlling    the crystallographic texture of Co-based alloys: Seedlayers may be    composed of amorphous or fine grain material such as NiAl, CrTi,    CoW, NiP. Underlayers may be Cr-based alloys.-   3. Non-magnetic interlayer, IL, that could comprise an alloy    material selected from the group consisting of Co_(100-δ)Cr_(δ);    with one or more added elements selected from Pt, Ta, B, Mo, Ru, Nb,    Hf, Zr. May or may not be present.-   4. Magnetic layers with at least one or more Au, Ag-containing    layers: In general the magnetic layer/s could comprise an alloy    material of CoCr or CoCr with one or more added elements selected    from Pt, Ta, B, Mo, Si, Cu, Ag, Au, Ge, Nb, Hf, Zr, Ti, V, W, Fe and    Ni. Magnetic layer without Au and Ag will be called “non Au or    Ag-containing magnetic layer,” ML, and magnetic layers with Au and    Ag will be called “Au, Ag-containing magnetic layer,” AuAgML. Au,    Ag-containing magnetic layers, AuAgML, could comprise    Co_(100-x-y-z-δ-α-β)Cr_(x)Pt_(y)B_(z)Ta_(δ)Ag_(α)Au_(β) alloys where    x, y, z, α, β concentrations satisfy the following rule: x adjusted    so that media is magnetic and in general x<30, also, 0≦y≦30, 0≦z≦24,    0≦δ≦8, 0≦α≦8, 0≦β≦8, α+β>0. Au, Ag-containing magnetic layers may    also contain one or more elements selected from Si, Ti, V, Fe, Ni,    Ge, Zr, Nb, Mo, Ru, Hf and W. Amount of Cu in Au, Ag-containing    magnetic layers should preferably be less than 10 at. %    (Co_(100-x-y-x-δ-α-β)Cr_(x)Pt_(y)B_(z)Ta_(δ)Ag_(α)Au_(β)Cu_(γ),    γ≦10).

Preferably, the rules for x, y, z, δ, α, β could be the following:

-   Cr-rich layer: (a) 16≦x≦30 and 0≦z≦12;    -   (b) 16≦x≦30, 0≦z≦12, 0≦α≦10, 0≦β≦10;    -   (c) 16≦x≦30, 0≦y≦30, 0≦z12, 0≦δ≦8, 0≦α≦10, 0≦β≦10;-   Cr-poor layer: (a) 0≦x≦16 and 10≦z≦24;    -   (b) 0≦x≦16, 10≦z≦24 and 0≦α≦10, 0≦β≦10;    -   (c) 0≦x≦16, 0≦y≦30, 10≦z≦24, 0≦δ≦8, 0≦α≦10, 0≦β≦10.        More preferably, the possible designs of the magnetic recording        layer:-   i) magnetic recording media includes at least one magnetic layer    that does not contain Au or Ag, ML.-   ii) [ML/AuAgML]×n, where n=1 to 10-   iii) [Cr-rich AuAgML/Cr-poor AuAgML]×n, where n=1 to 10-   iv) [ML/Cr-rich AuAgML/Cr-poor AuAgML]×n, where n=1 to 10-   v) ML_(i1)/AuAgML_(j1)/ML_(i2)/AuAgML_(j2)/ML_(i3), where i₁, i₂,    i₃, j₁, j₂=1 to 10, i₁+i₂+i₃+j₁+j₂≧2-   vi) [ML]_(i1)[Cr-rich CuML]_(j)[ML]_(i2)[Cr-poor CuML]_(k)[ML]_(i3),    where i₁, i₂, i₃, j and k each=0 to 10 and i₁+i₂+i₃+j+k≧3    AFC media could comprise main (top) layer located closer to    recording head and stabilizing (bottom) layer anti-ferromagnetically    coupled across non-magnetic spacer layer. Top magnetic recording    layer may have any of the layer design specified above. Bottom    magnetic layer design may have layer structure    [ML]_(i1)[CuML]_(j)[ML]_(i2), where i₁, i₂, and j=0 to 10 and    i₁+i₂+j≧1. A space layer can include nearly a non-magnetic    composition, and may include Ru, Rh, Ir, Cr, Cu, Re, V and their    alloys.-   5) Protective carbon layer.

Perpendicular film structure includes:

-   -   1) Substrate: Al, Glass or Plastic.    -   2) An adhesion layer (AL), Example: Cr, CrTi, Ti, NiNb.    -   3) A soft underlayer (SUL), preferably a Fe-containing alloy        containing one ore more elements from Co, B, P, Si, C, Zr, Nb,        Hf, Ta, Al, Cu, Ag, Au, having a thickness in the range of about        10-400 nm, preferably in the range of about 40-200 nm.    -   4) Amorphous layer (AmL) may be present preferably if the soft        underlayer is not amorphous. Examples include Ti_(δ)Cr_(100-δ),        Ta_(δ)Cr_(100-δ)(30<δ<60), and amorphous compositions of NiTa,        NiNb, NiP, and CrZr. The thickness of AmL is in the range of        about 0-10 nm, preferably in the range of about 0.2-2 nm.    -   5) Fcc interlayer/s (IL), may optionally be present, comprising        one or more elements from Cu, Pt, Ag, Au, Ir, Rh, Re. Also, one        or more elements selected from B, C, Si, V, Cr, Mn, Fe, Co, Ni,        Cu, Ge, Nb, Mo, Rh, Pd, Ag, Ta, W, Ir, Pt, Au may also be        present.    -   6) Hcp interlayer/s with at least one hcp layer that contains at        least one oxide material. The amount of oxide is adjusted such        that the interlayer structures may include any combination of        Co-rich and (Ru, Ti, Zr, Hf, Re)-rich layer both with and        without of oxide. Co-rich layer could comprise Co or Co alloyed        with one or more elements selected from B, C, Si, Ti, V, Cr, Mn,        Fe, Ni, Cu, Ge, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Ir,        Pt, Au. (Ru, Ti, Zr, Hf, Re)-rich could comprise at least one of        Ru, Ti, Zr, Hf, Re with one or more elements selected from B, C,        Si, V, Cr, Mn, Fe, Co, Ni, Cu, Ge, Nb, Mo, Rh, Pd, Ag, Ta, W,        Ir, Pt, Au.

Magnetic layers with at least one or more Au, Ag-containing layers. Ingeneral the magnetic layer/s could comprise an alloy material selectedfrom the group consisting of CoCr; CoCr with one or more added elementsselected from Pt, Ta, B, Mo, Si, Cu, Ag, Au, Ge, Nb, Hf, Zr, Ti, V, W,Fe and Ni. Au, Ag-containing magnetic layers, AuAgML, compriseCo_(100-x-y-z-δ-α-β)Cr_(x) Pt_(y) B_(z) Ta_(δ) Ag_(α) Au_(β) alloyswhere x, y, z, α, β concentrations satisfy the following rule: xadjusted so that media is magnetic and in general x<30, also, 0≦y≦30,0≦z≦10, 0≦δ≦8, 0≦α≦8, 0≦β≦8, α+β>0. Au, Ag-containing magnetic layersmay also contain one or more elements selected from Si, Ti, V, Fe, Ni,Ge, Zr, Nb, Mo, Ru, Hf and W. The amount of Cu in Au, Ag-containingmagnetic layers should be less than 10 at. %(Co_(100-x-y-z-δ-α-β-γ)Cr_(x)Pt_(y)B_(z)Ta_(δ)Ag_(α)Au_(β)Cu_(γ), γ≦10).

Preferably, the rules for x, y, z, δ, α, β could be the following:

-   Cr-rich layer: (a) 16≦x≦30 and 0≦z≦6;    -   (b) 16≦x≦30, 0≦z≦6, 0≦α≦10, 0≦β≦10;    -   (c) 16≦x≦30, 0≦y≦30, 0≦z≦6, 0≦δ≦8, 0≦α≦10, 0≦β≦10;-   Cr-poor layer: (a) 0≦x≦16 and 10≦z≦24;    -   (b) 0≦x≦16, 5≦z≦10 and 0≦α≦10, 0≦β≦10;    -   (c) 0≦x≦16, 0≦y≦30, 5≦z≦10, 0≦δ≦8, 0≦α≦10, 0≦β≦10;        More preferably, the possible designs of the magnetic recording        layer:-   i) magnetic recording media includes at least one magnetic layer    that does not contain Au or Ag, ML.-   ii) [ML/AuAgML]×n, where n=1 to 10-   iii) [Cr-rich AuAgML/Cr-poor AuAgML]×n, where n=1 to 10-   iv) [ML/Cr-rich AuAgML/Cr-poor AuAgML]×n, where n=1 to 10-   v) ML_(i1)/AuAgML_(j1)/ML_(i2)/AuAgML_(j2)/ML_(i3), where i₁, i₂,    i₃, j₁, j₂=1 to 10, i₁+i₂+i₃+j₁+j₂≧2-   vi) [ML]_(i1)[Cr-rich CuML]_(j)[ML]_(i2)[Cr-poor CuML]_(k)[ML]_(i3),    where i₁, i₂, i₃, j and k each=0 to 10 and i₁+i₂+i₃+j+k≧3-   7) Protective carbon layer.

The embodiments of the invention provide magnetic recording mediasuitable for high a real recording density exhibiting high SMNR. Theembodiments of the invention achieve such technological advantages byforming a soft underlayer. A “soft magnetic material” is a material thatis easily magnetized and demagnetized. As compared to a soft magneticmaterial, a “hard magnetic” material is one that neither magnetizes nordemagnetizes easily.

The underlayer is “soft” because it is made up of a soft magneticmaterial, which is defined above, and it is called an “underlayer”because it resides under a recording layer. In a preferred embodiment,the soft layer is amorphous. The term “amorphous” means that thematerial of the underlayer exhibits no predominant sharp peak in anX-ray diffraction pattern as compared to background noise. The“amorphous soft underlayer” of the embodiments of the inventionencompasses nanocrystallites in amorphous phase or any other form of amaterial so long the material exhibits no predominant sharp peak in anX-ray diffraction pattern as compared to background noise.

When soft underlayers are fabricated by magnetron sputtering on disksubstrates, there are several components competing to determine the netanisotropy of the underlayers: effect of magnetron field,magnetostriction of film and stress originated from substrate shape,etc. The soft magnetic underlayer can be fabricated as single layers ora multilayer.

A seedlayer could be optionally included in the embodiments of thisinvention. A seedlayer is a layer lying in between the substrate and theunderlayer. Proper seedlayer can also control anisotropy of the softunderlayer by promoting microstructure that exhibit either short-rangeordering under the influence of magnetron field or differentmagnetostriction. A seedlayer could also alter local stresses in thesoft underlayer.

Preferably, in the underlayer of the perpendicular recording medium ofthe embodiments of the invention, an easy axis of magnetization isdirected in a direction substantially transverse to a travelingdirection of the magnetic head. This means that the easy axis ofmagnetization is directed more toward a direction transverse to thetraveling direction of the read-write head than toward the travelingdirection. Also, preferably, the underlayer of the perpendicularrecording medium has a substantially radial or transverse anisotropy,which means that the domains of the soft magnetic material of theunderlayer are directed more toward a direction transverse to thetraveling direction of the read-write head than toward the travelingdirection. In one embodiment, the direction transverse to the travelingdirection of the read-write head is the direction perpendicular to theplane of the substrate of the recording medium.

In accordance with embodiments of this invention, the substrates thatmay be used in the embodiments of the invention include glass,glass-ceramic, NiP/aluminum, metal alloys, plastic/polymer material,ceramic, glass-polymer, composite materials or other non-magneticmaterials. Glass-ceramic materials do not normally exhibit a crystallinesurface. Glasses and glass-ceramics generally exhibit high resistance toshocks.

A preferred embodiment of this invention is a perpendicular recordingmedium comprising at least two amorphous soft underlayers with a spacerlayer between the underlayers and a recording layer. The amorphous softunderlayer should preferably be made of soft magnetic materials and therecording layer should preferably be made of hard magnetic materials.The amorphous soft underlayer is relatively thick compared to otherlayers. The interlayer can be made of more than one layer ofnon-magnetic materials. The purpose of the interlayer is to prevent aninteraction between the amorphous soft magnetic underlayer and recordinglayer. The interlayer could also promote the desired properties of therecording layer.

The underlayer and magnetic recording layer could be sequentiallysputter deposited on the substrate, typically by magnetron sputtering,in an inert gas atmosphere. A carbon overcoat could be typicallydeposited in argon with nitrogen, hydrogen or ethylene. Conventionallubricant topcoats are typically less than about 20 Å thick.

Amorphous soft underlayers could produce smoother surfaces as comparedto polycrystalline underlayers. Therefore, amorphous soft underlayercould be one way of reducing the roughness of the magnetic recordingmedia for high-density perpendicular magnetic recording. The amorphoussoft underlayer materials include a Cr-doped Fe-alloy-containingunderlayer, wherein the Fe-alloy could be CoFeZr, CoFeTa, FeCoZrB andFeCoB.

Another advantage of amorphous materials as soft underlayer materials isthe lack of long-range order in the amorphous material. Without along-range order, amorphous alloys have substantially nomagnetocrystalline anisotropy. The use of amorphous soft underlayercould be one way of reducing noise caused by ripple domains and surfaceroughness. The surface roughness of the amorphous soft underlayer ispreferably below 1 nm, more preferably below 0.5 nm, and most preferablybelow 0.2 nm.

In accordance with the embodiments of the invention, the test methodsfor determining different parameters are as follows. If a particulartest method has not been explicitly stated below to determine aparameter, then a conventional method used by persons of ordinary skillin this art could be used to determine that parameter.

Coercivity (H_(c)): In the embodiments of this invention, the preferredrange of H_(c) is 2500 to 9000, more preferably 4000 to 7000 Oe.

Mrt: Product of remanent magnetization and magnetic layer thickness: Inthe embodiments of this invention, the preferred range of Mrt is 0.2-1memu/cm², more preferably, 0.30-0.7 memu/cm².

S*: Slope of remanence magnetization curve dMr/dH at the point whereMr=0.

MFA: middle frequency amplitude.

LFA: low frequency amplitude.

PW50 is measure of transition width (between two written bits). In theembodiments of this invention, a lower PW50 value is preferred.

OW means overwrite. In the embodiments of this invention, the preferredrange of OW includes high values.

SNRmed: Media signal to noise ratio. In the embodiments of thisinvention, the preferred range of SNRmed includes high values.

SNRel: Electronic signal to noise ratio. In the embodiments of thisinvention, the preferred range of SNRel includes high values.

SNRtot: Total signal to noise ratio. In the embodiments of thisinvention, the preferred range of SNRtot is a higher value.

The advantageous characteristics attainable by the embodiments of theinvention are illustrated in the following examples.

EXAMPLES

All samples described in this disclosure were fabricated with DCmagnetron sputtering except carbon films were made with AC magnetronsputtering.

Applicants investigated investigated the following media structures:

-   Media 1. Substrate/UL/BL/Ru/ML₁/ML(Co—Cr—Pt—B)-   Media 2. Substrate/UL/BL/Ru/ML₁/CuML(Co—Cr—Pt—B—Cu)-   Media 3. Substrate/UL/BL/Ru/ML₁/AuAgML(Co—Cr—Pt—B—Ag)-   Media 4. Substrate/UL/BL/Ru/ML₁/AuAgML(Co—Cr—Pt—B—Au)

In the above media investigated, Cr in ML(Co—Cr—Pt—B) is substituted byCu, Ag and Au in CuML(Co—Cr—Pt—B—Cu), AuAgML(Co—Cr—Pt—B—Ag) andAuAgML(Co—Cr—Pt—B—Au), respectively. The recording data are presented inTable 1. Table 1 shows that recording performance of magnetic media canbe improved by substituting Cu, Ag and Au for Cr, i.e., by addition ofCu, Ag and Au to magnetic recording layers: Signal to noise ratio ofmedia (SNRmed) with AuAgML(Co—Cr—Pt—B—Au) magnetic layer, media 4, is˜0.7 dB higher than SNRmed of recording media withoutAuAgML(Co—Cr—Pt—B—Au) magnetic layer, media 1.

TABLE 1 H_(C) MrT MFA LFA PW50 OW SNRmed SNRel SNRtot [Oe] [memu/cm²] S*[mV] [mV] [μinch] [dB] [dB] [dB] [dB] Media 1 4657 0.33 0.86 1.16 1.463.4 36.0 14.5 16.2 12.3 Media 2 (Cu) 4516 0.32 0.86 1.16 1.45 3.4 37.315.1 16.2 12.6 Media 3 (Ag) 4354 0.34 0.86 1.25 1.57 3.5 40.0 14.7 16.412.5 Media 4 (Au) 4643 0.31 0.85 1.18 1.47 3.3 37.6 15.2 16.4 12.8

Applicants measured a lattice constant of ML(Co—Cr—Pt—B),CuML(Co—Cr—Pt—B—Cu), AuAgML(Co—Cr—Pt—B—Ag) and AuAgML(Co—Cr—Pt—B—Au)magnetic layers. Table 2 shows that the lattice constant a ofML(Co—Cr—Pt—B) does not change if Cr is substituted by Cu, Ag and Au.This indicates that Ag and Au do not substitute for Co (or Cr ifpresent) in CoPt rich magnetic grains. Ag and Au atoms are significantlybigger than Co atom so they would expand lattice constants of magneticgrains if they replace Co (or Cr if present) in these grains.

TABLE 2 Co Atom diameter a = [11-20] [nm] λ/sinθ [nm] CuML(CoCrPtB)73.15 Co = 0.250, 0.2588 Pt = 0.278, Cr = 0.260 CuML(CoCrPtBCu) 72.98 Cu= 0.256 0.2593 AuAgML(CoCrPtBAg) 73.08 Ag = 0.288 0.2590AuAgML(CoCrPtBAu) 72.95 Au = 0.292 0.2594

Applicants also measured the saturation magnetization, Ms, ofML(Co—Cr—Pt—B), CuML(Co—Cr—Pt—B—Cu), AuAgML(Co—Cr—Pt—B—Ag) andAuAgML(Co—Cr—Pt—B—Au) magnetic layers. Table 3 shows ˜12% increase in Msif Cr is substituted by Ag or Au and ˜5% increase in Ms if Cr issubstituted by Cu.

TABLE 3 M_(s) [emu/cm³] CuML(CoCrPtB) 243 CuML(CoCrPtBCu) 257AuAgML(CoCrPtBAg) 275 AuAgML(CoCrPtBAu) 275

It follows from Table 2 and Table 3 and FIG. 1 that Ag and Au mainlysegregate in the grain boundary regions. Cu position in the magneticlayer is not certain. However, only Au likes to mix with Cr(B) that canlead to more uniformly distribution of Au in the grain boundary regions.Thus it is expected that Au will provide better magnetic grain isolationin CoCrPtB magnetic layers than Ag and Cu resulting in improved mediaperformance, see Table 3.

This application discloses several numerical range limitations thatsupport any range within the disclosed numerical ranges even though aprecise range limitation is not stated verbatim in the specificationbecause this invention can be practiced throughout the disclosednumerical ranges. Finally, the entire disclosure of the patents andpublications referred in this application are hereby incorporated hereinin entirety by reference.

1. A magnetic recording medium comprising a substrate and aperpendicular magnetic recording layer on the substrate, wherein themagnetic recording layer comprises the following layers, in order: afirst layer comprising an alloy comprising Co, Cr, Pt, and B; a secondlayer, different from the first layer, wherein the second layercomprises an alloy comprising Co, Cr, Pt, B, and ≦10 at. % but >0 at. %,of at least one of Au and Ag, wherein the second layer comprises ≧16 at.% and ≦30 at. % Cr, ≦30 at. % Pt, and ≦6 at. % B; and a third layer,different from the first and second layers, the third layer comprisingan alloy comprising Co, Cr, Pt, B, and ≦10 at. % but >0 at. %, of atleast one of Au and Ag, wherein the alloy in the third layer comprises≦16 at. % Cr, ≦30 at. % Pt, and ≧5 at. % and ≦10 at. % B.
 2. Themagnetic recording medium of claim 1, wherein the magnetic recordinglayer comprises n sets of [(first layer)(second layer)(third layer)],and wherein n=1 to
 10. 3. The magnetic recording medium of claim 1,wherein the alloy in any of the layers in the magnetic recording mediumfurther comprises Ta.
 4. The magnetic recording medium of claim 1,wherein the alloy in the first layer is CoCrPtB and the alloy in eitherof the second and third layers is CoCrPtBAg.
 5. The magnetic recordingmedium of claim 4, wherein the alloy in either of the second and thirdlayers is CoCrPtBAu.
 6. The magnetic recording medium of claim 1,wherein the alloy in either of the second and third layers furthercomprises Ta, and Ta is present in the alloy at ≦8 at %.
 7. The magneticrecording medium of claim 1, wherein the alloy in the first layerfurther comprises an element selected from the group consisting of Mo,Si, Ge, Nb, Hf, Zr, Ti, V, W, Fe, Ni and combinations thereof.
 8. Themagnetic recording medium of claim 1, wherein the alloy in either of thesecond and third layer further comprises an element selected from thegroup consisting of Si, Ti, V, Fe, Ni, Ge, Zr, Nb, Mo, Ru, Hf, W andcombinations thereof.
 9. A magnetic recording medium comprising asubstrate and a perpendicular magnetic recording layer on the substrate,wherein the magnetic recording layer consists of n pairs of thefollowing layers, with n=1 to 10: a first layer comprising an alloycomprising Co, Cr, Pt, B, and ≦10 at. % but >0 at. %, of at least one ofAu and Ag, wherein the alloy in the first layer comprises ≧16 at. % and≦30 at. % Cr, ≦30 at. % Pt, and ≦6 at. % B, and a second layer,different from the first layer, the second layer comprising an alloycomprising Co, Cr, Pt, B, and ≦10 at. % but >0 at. %, of at least one ofAu and Ag, and wherein the alloy in the second layer comprises ≦16 at. %Cr, ≦30 at. % Pt, and ≧5 at. % ≦10 at. % B.
 10. A magnetic recordingmedium, comprising: (a) a substrate; (b) a first amorphous layer,wherein the first amorphous layer comprises an Fe alloy; (c) a secondamorphous layer different from the first amorphous layer, wherein thesecond amorphous layer comprises at least one of TiCr, TaCr, NiTa, NiNb,NiP and CrZr; (d) a perpendicular magnetic recording layer with thefollowing layers, in order: (1) a first layer comprising an alloycomprising Co, Cr, Pt, and B; a second layer, different from the firstlayer, wherein the second layer comprises an alloy comprising Co, Cr,Pt, B, and ≦10 at. % but >0 at. %, of at least one of Au and Ag, whereinthe second layer comprises ≧16 at. % and ≦30 at. % Cr, ≦30 at. % Pt, and≦6 at. % B; and a third layer, different from the first and secondlayers, the third layer comprising an alloy comprising Co, Cr, Pt, B,and ≦10 at. % but >0 at. %, of at least one of Au and Ag, wherein thealloy in the third layer comprises ≦16 at. % Cr, ≦30 at. % Pt, and ≧5at. % and ≦10 at. % B; or (2) a first layer comprising an alloycomprising Co, Cr, Pt, B, and ≦10 at. % but >0 at. %, of at least one ofAu and Ag, wherein the alloy in the first layer comprises ≧16 at. % and≦30 at. % Cr, ≦30 at. % Pt, and ≦6 at. % B, and a second layer,different from the first layer, the second layer comprising an alloycomprising Co, Cr, Pt, B, and ≦10 at. % but >0 at. %; and of at leastone of Au and Ag, and wherein the alloy in the second layer comprises≦16 at. % Cr, ≦30 at. % Pt, and ≧5 at. % and ≦10 at. % B; and (e) atleast one interlayer between the second amorphous layer and the magneticrecording layer.
 11. The magnetic recording medium of claim 10, whereinthe interlayer is selected from the group consisting of a Fccinterlayer, a Hcp interlayer, and combinations thereof.
 12. The magneticrecording medium of claim 11, wherein the interlayer is an Fccinterlayer, and wherein the Fcc interlayer comprises one or moreelements selected from the group consisting of Cu, Pt, Ag, Au, Ir, Rh,and Re.
 13. The magnetic recording medium of claim 11, wherein the Hcpinterlayer comprises at least one oxide, and wherein the Hcp interlayercomprises at least one of Co, Ru, Ti, Zr, Hf and Re.